Fiber optic array

ABSTRACT

A fiber optic array is disclosed for use in an optical scanning device. The array includes a substrate and rows of optical fibers stacked on the substrate. The optical fibers are all of a predetermined diameter. In order to precisely space the fibers relative to each other, the fibers in the first row are arranged in grooves in the substrate, and each succeeding row of fibers is disposed on the fibers of the preceding row.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned U.S. patent application, Ser. No.440,159, entitled "Method of Making A Fiber Optic Array," filed on evendate herewith, in the name of Kaukeinen.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fiber optic array, and moreparticularly, to such an array which is used in an optical scanningdevice.

2. State of the Prior Art

It is known in the prior art to use an array of optical fibers in aprint head which is used to record information on a light-sensitiverecording medium. The fibers can be arranged with their output ends in alinear array extending in a direction transverse to the direction ofmovement of the recording medium, and a light source, such as alight-emitting diode or a diode laser, can be connected to each of thefibers at an input end. The light in each of the fibers is modulated inaccordance with an information signal to produce a desired image.Focusing means can be used in front of each fiber to cause the light tobe focused to a point on the recording medium. It is desirable for thearrays of optical fibers to have a high packing density, i.e., a highnumber of fibers per unit width of the array, in order to limit theamount of data buFfering needed to produce the output image. There is aproblem, however, in using increasingly thinner fibers to increase thepacking density. As the fibers are made thinner, handling and alignmentof the fibers becomes more difficult, and the thinner fibers are morelikely to break in the assembly process.

Another method of increasing the packing density of optical fiber arraysis to use multiple layers, or rows, of fibers, as shown, for example, inU.S. Pat. No. 4,389,655, to Baues. In the Baues patent, there is shownan optical device for non-impact recording in which the recording headincludes a linear array of optical fibers. The recording head comprisesan adjustment plate having a plurality of grooves therein, and anoptical fiber is secured in each of the grooves to form a first row offibers. A second row of fibers is arranged above the first row, and thefibers in the top row are offset relative to the fibers in the bottomrow. The second row of fibers is also supported in grooves in a secondadjustment plate, with the grooves of the second adjustment plate facingthe grooves of the first adjustment plate. A problem with thisarrangement is that it is very difficult to get the proper spacingbetween the rows of optical fibers. A further problem is that the arrayis limited to only two layers, and it is advantageous to have more thantwo layers in certain applications.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the problems in theprior art noted above and to provide an improved fiber optic array foruse in scanning devices.

In accordance with one aspect of the invention, there is provided afiber optic array comprising: a substrate which is adapted to supportoptical fibers on a surface thereof, the substrate including a pluralityof side-by-side grooves therein; at least two rows of optical fiberssupported on the substrate, a first row of optical fibers beingsupported in the grooves and a second row of optical fibers beingdisposed on the first row, each of the optical fibers in the second rowbeing disposed on two adjacent fibers in the first row, all of thefibers being of a predetermined diameter, and the spacing of the opticalfibers in the second row being determined by the spacing of the groovesand the diameter of the fibers.

The fiber optic array of the present invention includes an array ofoptical fibers having a plurality of rows of fibers, and a first row ofthe fibers are supported in grooves formed in a substrate. The groovesare arranged in aligned sets, and each set of grooves is separated byplanar areas on the substrate which are coplanar with the bottoms of thegrooves. At an input end of the substrate is a set of grooves which aresized to receive the jackets of the optical fibers; and sets of grooves,which are sized to receive the cladding of the fibers, are spaced alongthe substrate and extend to an output end of the substrate. The pitch ofthe grooves in successive sets decreases as the fibers approach theoutput end of the substrate in order to draw the fibers closer togetherat the output end.

In one embodiment of the present invention, closely spaced V-shapedgrooves are etched in a silicon substrate. An optical fiber is insertedin each of the grooves to form the first row in a linear array offibers. An adhesive is used to secure the fibers in the grooves inselected areas of the substrate. A second row of optical fibers isplaced in a substrate of a reduced length so that the fibers extend fromone end thereof. The substrate containing the second row is placed overthe substrate containing the first row such that the fibers extendingfrom the one end are placed over the fibers in the first row located atthe output end of the array. At the output end of the array, each fiberin the second row is disposed between two adjacent fibers in the firstrow. Additional rows of fibers can be added if they are needed for aparticular application, and after the desired number of rows have beenstacked, an adhesive is introduced into the interstices of the orderedrows of fibers. In one embodiment of the present invention, opticalfibers having a cladding end portion of reduced diameter are used inorder to increase the packing density.

A principal advantage of the array of the present invention is that avery high packing density is obtained as a result of stacking the fibersin multiple rows. Each row of optical fibers, after the first row, isaligned by the fibers in the preceding row. It is possible to controlthe amount of overlap of spots produced on a recording medium byselecting the spacing of the grooves in the substrate. Another advantageof the array of the present invention is that the optical fibers can besupported on the substrate in close proximity to each other in a mannerwhich does not damage the fibers nor affect the performance of thefibers. A further advantage of one embodiment of the present inventionis that increased packing density can be obtained as a result of usingfibers in which the cladding diameter at one end is relatively small.Outputs from the closely-spaced and independently-addressable fibers canbe imaged onto a receiving medium through a single train of optics withdiffraction-limited performance.

Other features and advantages will become apparent with reference to thefollowing Description of the Preferred Embodiments when read in light ofthe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an end portion of the fiber optic arrayof the present invention;

FIG. 2 is a front elevational view of the array shown in FIG. 1;

FIG. 3 is a plan view of a substrate for the array of the presentinvention;

FIG. 4 is a view of an optical fiber in which the jacket has beenremoved from a portion thereof;

FIG. 5 is a view of an optical fiber which can be used in a secondembodiment of the present invention;

FIGS. 6A-6B are sectional views taken along the lines 6A--6A, 6B--6B,and 6C--6C, respectively, in FIG. 3;

FIG. 7 is an front elevational view of an array in which the opticalfibers are arranged to produce overlapping spots; and

FIG. 8 is sectional view of an array in which a substrate is used tosupport the fibers in the second row.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 1, there is shown an end portion of a fiber opticarray 10 which comprises a first row 11 of optical fibers 12 which aresupported on a substrate 16. A second row 15 of optical fibers 12 aresupported on the fibers 12 in row 11, and a third row 17 of fibers 12are supported on the fibers 12 in row 15. A glass plate 40 extends overthe fibers 12 in row 17, and an epoxy (not shown) fills the void areasbetween plate 40 and substrate 16.

As discussed hereinafter, fibers 12 in rows 15 and 17 can also besupported on substrates which facilitate the assembly of the array. Eachof the fibers 12 can be connected to a light source (not shown) such asa diode laser or a light smitting diode, and the light source can bemodulated according to an information signal in a well known manner.Array 10 can be used to record information on a light-sensitive medium(not shown) such as a photoconductor or photographic film. Array 10 canalso be used as an optical scanner (not shown) in which light reflectedfrom an object is transmitted through the optical fibers tophotosensitive elements.

As shown in FIG. 4, each of the optical fibers 12 includes a jacket 30,a cladding 32, and a core 34. In a preferred form of the presentinvention, the jacket 30 is removed from a portion of the fiber toexpose the cladding 32, as shown in FIG. 4; however, the array of thepresent invention could be formed with optical fibers in which thejackets extend through the entire length of the fiber. The array 12could also be formed with optical fibers, as shown in FIG. 5, in whichthe diameter of the cladding in a portion 33 is substantially reduced sothat the fibers can be more closely spaced relative to each other. Atapered portion 36 is formed between the portion 33 and the cladding 32.A more complete description of a fiber having an end portion of areduced diameter and of the method of making such a fiber can be foundin the U.S. application, Ser. No. 254,757, filed Oct. 7, 1988, whichissued as U.S. Pat. No. 4,923,275, and the disclosure of thisapplication is expressly incorporated herein by reference. A fibersuitable for use in the present invention is a special single mode fibermade by Corning Glass Works, Fiber No. 56704121,KH1. This fiber is madeof silica with germanium doping in the core 34. The jacket 30 has adiameter of 250 μm, the cladding 32 has a diameter of 125 μm, and thecore 34 has a diameter of 4 μm. Other optical fibers can be used withthe present invention, including multi-mode fibers.

Fibers 12 extend in array 10 from an input end 21 of substrate 16 (FIG.3) which supports jackets 30 of the fibers to an output end 22 of thesubstrate 16, and the fibers 12 are closest together at end 22. In orderto form the array 10 with the fibers 12 precisely spaced relative toeach other at output end 22, all of the fibers 12 must be of the samediameter within a very small tolerance, for example, within ±1 μm.Fibers 12 are mounted in sets of grooves 28a-28g which are formed insubstrate 16 and are separated by planar areas 29a-29f in the substrate16. Grooves 28a-28g in each set are separated by lands 25a-25g,respectively. Grooves 28a are generally rectangular in cross section, asshown in FIG. 6A, and grooves 28b-28g are generally V-shaped in crosssection as shown in FIG. 6B. In a preferred embodiment, the areas29a-29f (FIGS. 3 and 6C) are coplanar with the bottoms of adjacentgrooves; one of the groove bottoms is shown at 27b in FIG. 6B.

Grooves 28a-28g are arranged to space fibers 12 progressively closertogether in the direction of output end 22 of the substrate 16. Theprogressively closer spacing is accomplished by decreasing the pitch p(FIG. 6B) of the grooves in successive sets of grooves 28a-28g. As shownin FIG. 6B, the pitch p of the grooves includes the width W of thegrooves and width S of the lands 25a-25g. The pitch p can be changed bychanging the width S of the land, or by changing the width W of thegrooves, or by changing both S and W.

Grooves 28a are sized to receive the jackets 30 of fibers 12. Grooves28b-28g are adapted to receive the cladding 32 of the fibers 12. It isimportant that the jackets 30 remain on fibers 12 for a certain lengthon substrate 16 to lend stability to array 10. The dimensions of thegrooves 28a-28g will depend on the size and type of fiber used in array10. For a single mode fiber of the type described above, obtainable fromCorning Glass Works, the grooves 28a can be from about 255 μm to about280 μm wide, and grooves 28b-28g can be about 155 μm wide. The includedangle of the grooves 28b-28g is about 70° when the grooves are etched insilicon. Starting with grooves 28b and progressing through successivesets of grooves 28g, the grooves 28b-28g are separated by lands 25b-25ghaving progressively thinner widths S in order to draw the fibers 12closer together at end 22 of the substrate 16. For example, the widths Sof the lands 25 a-25g can be, respectively, 250, 100, 76, 53, 29, 5, and4 μm. As noted above, fibers 12, as shown in FIG. 5, having portions 33of reduced diameter can be used; for fibers 12 of this type, thedimensions of grooves 28g will depend on the diameter of the portion 33.For example, for diameters of portion 33 which range from 10 μm to 100μm, the width of grooves range from 12 μm to 146 μm, respectively.

In one illustrative example of the present invention, the length of thesubstrate 16 is about 75 mm, the width of the substrate is about 25 mm,and the substrate is about 525 μm thick. The length of the grooves 28ais about 10 mm, the length of grooves 28b-28f is about 2 mm, and thelength of grooves 28g is about 25 mm. The length of planar areas 29a-29eis about 4 mm, and the length of planar area 29f is about 10 mm.

The substrate 16 is preferably formed from a silicon wafer (not shown)by photolithographic means. A suitable mask (not shown) is used to formthe grooves 28b for a plurality of substrates 16 on the wafer. The waferis cleaned before and after etching using acetone and deionized water,and the wafer is then blown dry with nitrogen. The etching agent is a12% potassium hydroxide (KOH) solution with a bath temperature ofapproximately 62° C. This results in an etching rate in groove depth ofapproximately 0.29 μm/min. A more complete description of the method offorming the substrate 16 can be found in the aforementioned U.S. patentapplication, Ser. No. 254,757.

Great care must be used in the mounting of fibers 12 on substrate 16 dueto the fragility and relatively small size of the fibers. In a firststep, the fibers 12 are arranged parallel to each other in a holder (notshown) having channels to receive the jackets 30. The jackets 30 of thealigned fibers 30 are then inserted in the grooves 28a on substrate 16.A teflon-coated glass plate (not shown) is placed over the jackets 30 ingrooves 28a. The glass plate can be about 150 μm thick and should be ofa size to extend over grooves 28a. The glass plate is held in place by aneedle in a micropositioner, model 221, obtainable from Rucker andKolls. An ultraviolet light curable epoxy is introduced between theglass plate and substrate 16, and the epoxy is drawn into grooves 28aaround the jackets 30 of fibers 12 by means of capillary action. Theepoxy is partially cured by ultraviolet light which is directed onto theepoxy through the teflon-coated the glass plate. The teflon-coated glassplate is then removed, and the epoxy is fully cured by additionalultraviolet light.

In a next step, the cladding 32 of fibers 12 is eased into grooves28b-28g of progressively finer pitch, and the fibers 12 are cemented inplace in each set of grooves 28b-28f by means of a teflon-coated glassplate and UV curable epoxy as described previously; that is, the glassplate is placed directly over the fibers 12 in the grooves, held inposition by a micropositioner, and UV curable epoxy is introduced aroundthe fibers 12 in the grooves by means oF capillary action. The fibers inthe set of grooves 28g are cemented only at an end portion in order tofacilitate the mounting of row 15 on row 11. The teflon-coated glassplate is removed after the epoxy has been partially cured, and full cureis then established with additional UV light.

The planar areas 29a-29f provide an area in which the fibers 12 aredrawn closer together between the sets of generally parallel grooves28b-28g of progressively smaller pitch. The planar areas 29a-29f arealso important in the assembly steps just described in that they providea means for viewing the fibers to determine if the fibers are actuallyaligned, since it is very difficult to see the fibers in the sets ofgrooves 28b-28g. The planar areas also provide a barrier to thecapillary flow of adhesive so that the fibers can be attached to aparticular set of grooves independently of adjacent sets of grooves.

In a preferred method of forming row 15, fibers 12 are assembled in asubstrate 26 (FIG. 8) in the manner just described for substrate 16.Substrate 26 is identical to substrate 16 except that substrate 26 doesnot include a portion comparable to the portion of substrate 16 thatincludes planar area 29f and grooves 28g. Thus, the fibers 12 onsubstrate 26 extend beyond the end of the substrate 26 to facilitate theassembly of fibers 12 of row 15 on the fibers in row 11. When the fibershave been assembled on substrate 26, the substrate 26 is placed oversubstrate 16, as shown in FIG. 8. The fibers 12 in row 15 are cementedto the fibers 12 in row 11 at a point A (FIG. 8), using a UV curableepoxy and a teflon coated glass plate 42; cementing the fibers at pointA aids in alignment of the fibers at a point B. A glass plate 40 isplaced over the two rows of fibers 11 and 15 at point B, and the glassplate is held in place by a pin attached to a micropositioner. UVcurable epoxy is then introduced under the glass plate, and the epoxy iscured. A cross groove (not shown) in substrate 16, which extendsperpendicular to the direction of the fibers 12, can be used to aid inthe introduction of the epoxy in the grooves holding the fibers 12. Whenthe fibers 12 have been cemented in place, a portion of the array facet19 is removed by means of a dicing saw (not shown), and the facet 19 isthen polished. The dicing saw can be a resin impregnated diamond blade,and the dicing step can be accomplished by cutting through the assemblyat, for example, point B (FIG. 8).

In the forming of an array having a third row 17, the fibers 12 of row17 can be mounted in another substrate 26 (not shown). The substrate andfibers are then placed over the substrate and fibers which form row 15,and the fibers of row 17 are cemented to the fibers of row 15 at a pointjust above point A. A glass plate 40 is then placed on the fibers in row17, and the cementing and dicing steps described above are repeated. Inthis arrangement, the array includes a stack of three rows of fibers,row 11 being supported on substrate 16, row 15 being supported on asubstrate 26, and row 17 being supported on a substrate 26 (not shown).

In an alternative arrangement, it is possible, with careful alignment ofthe fibers, to form an array in which the individual fibers 12 of row 15are cemented directly to the fibers in row 11 using a UV curable epoxy.A substrate 26 with fibers 12 thereon is then mounted over the fibers 12in row 15, in the manner described above, to form row 17. In thisarrangement, the array has three rows of fibers, one substrate 16 andone substrate 26.

An important element of the present invention is the adhesive used tocement the fibers to the substrate. The adhesive must have low viscosityfor food capillary action and a lower refractive index than that of thecladding to minimize radiation loss and cross talk between fibers. Afterthe adhesive has cured, there should be low stress on the fiber tominimize micro-bending loss, and the adhesive should have adequatehardness to insure a polished surface of high quality. One suitableadhesive is Norland 61 adhesive which can be obtained from the NorlandCo. However, a preferred adhesive is Lamdek U V Adhesive, Catalog No.177 6921, obtainable from Dymax Engineering Adhesives, a division ofAmerican Chemical and Engineering Co., Torrington, Conn.

In an illustrative example of the present invention, an array 10 wasformed from single mode fibers having a core diameter of about 4 μm anda cladding diameter of about 125 μm. The fibers 12 were mounted in themanner described above to form an array of three rows of fibers as shownin FIG. 1.

It will be apparent that the number and spacing of fibers 12 can bechanged to meet the needs of a particular application. An array (notshown) could extend the full length of a recording medium, or arecording head (not shown) could include a plurality of arrays arrangedside-by-side or in parallel rows.

An array 10 can also be used to produce various print formats and toproduce various effects on the recording medium. In FIG. 7, for example,there is shown an array 10' of optical fibers 12' in which the pitch pof the grooves 28g' has been made relatively small in order to achievean overlap in the spots produced from the fibers 12 on a recordingmedium (not shown). In raster scanning printing systems, the spots mayneed to overlap to reduce the raster line visibility. If a gaussianintensity light source is used, the overlap may need to be on the orderof 40% of the spot size. By adjusting the pitch of the grooves and thefiber diameter D, the desired overlap of the focused spots on therecording medium can be achieved. With reference to the arrays 10 and10', shown in FIGS. 2 and 7, respectively, it will be seen that when thepitch p is reduced, the spacing between adjacent fibers in the same rowis reduced and the spacing s₁, in a scan direction, between the centersof adjacent fibers 12 in adjacent rows is also reduced. Further, whenthe pitch p is reduced, the spacing s₂, in a cross-scan direction,between the centers of fibers 12 in adjacent rows is increased. Thus, itwill be seen that spacing of the fibers needed to produce a desiredoverlap of the spots for a particular application can be controlled byselecting the fiber diameter D and the pitch of the grooves formed inthe substrate 16.

The invention has been described in detail with particular reference toa preferred embodiment thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:
 1. A fiber optic array comprising:a first substrate which isadapted to support optical fibers on a surface thereof, said substrateincluding a plurality of sets of generally parallel grooves therein,said grooves being generally V-shaped and each set of grooves beingseparated from the other sets of grooves by an area on said surface; andat least two rows of optical fibers supported on said substrate, a firstrow of optical fibers being supported in said grooves and a second rowof optical fibers being disposed on said first row, each of the opticalfibers in said second row being disposed on two adjacent fibers in saidfirst row, all of said fibers being of a predetermined diameter, and thespacing of the optical fibers in said second row being determined by thespacing of said grooves and the diameter of said fibers.
 2. A fiberoptic array, as defined in claim 1, wherein said sets of grooves are ingeneral alignment.
 3. A fiber optic array, as defined in claim 2,wherein said areas are generally planar.
 4. A fiber optic array, asdefined in claim 1, wherein said sets of grooves are spaced along saidsubstrate from one end to an opposite end thereof, and the pitch of saidgrooves is less at said opposite end of the substrate than at said oneend such that the fibers therein converge toward said opposite end.
 5. Afiber optic array, as defined in claim 1, wherein the grooves of one ofsaid sets are sized to receive cladding on said fibers.
 6. A fiber opticarray, as defined in claim 1, wherein said second row of fibers issupported by a second substrate.
 7. A fiber optic array, as defined inclaim 6, wherein said second substrate is shorter than said firstsubstrate.
 8. A fiber optic array comprising:a substrate which isadapted to support optical fibers on a surface thereof, said substrateincluding a plurality of sets of side-by-side grooves therein, each ofsaid sets being generally aligned with the other sets and separated fromthe other sets by an area on said surface; and at least two rows ofoptical fibers supported on said surface, a first row of optical fibersbeing supported in said grooves and a second row of optical fibers beingdisposed on said first row.
 9. A fiber optic array, as defined in claim8, wherein the pitch of each of said sets is different from the othersets.
 10. A fiber optic array, as defined in claim 9, wherein each ofsaid areas is generally coplanar with a bottom portion of said grooves.11. A fiber optic array comprising:a substrate which is adapted tosupport optical fibers on a surface thereof, said substrate including aplurality of sets of side-by-side grooves therein, each of said setsbeing generally aligned with the other sets and separated from the othersets by an area on said surface, the grooves in one of said sets beinggenerally rectangular in cross section and the grooves in the rest ofsaid sets being generally V-shaped in cross section; and at least tworows of optical fibers supported on said surface, a first row of opticalfibers being supported in said grooves and a second row of opticalfibers being disposed on said first row, jackets of the fibers in saidfirst row being supported in the grooves of said one set and exposedcladding of said fibers in the first row being supported in the groovesof the rest of said sets.
 12. A fiber optic array comprising:a firstsubstrate which is adapted to support optical fibers on a surfacethereof, said substrate including a plurality of side-by-side groovestherein; and at least two rows of optical fibers supported on saidsubstrate, a first row of optical fibers being supported in said groovesand a second row of optical fibers being disposed on said first row,each of the optical fibers in said second row being disposed on twoadjacent fibers in said first row such that the spacing of the opticalfibers in said second row is determined by the spacing of said groovesand the diameter of said fibers, each of said optical fibers includingan exposed length of cladding, and an end portion of said exposed lengthof cladding having an outside diameter which is less than the outsidediameter of the remainder of said exposed length of cladding.